Device and method for the packet based access of classical isdn/pstn subscribers to a switching system

ABSTRACT

The invention relates to a device and to a method for the packet-based access of classical ISDN/PSTN subscribers to a switching system. The convergence of packet-based networks and TDM networks leads to a situation where classical analogous and ISDN subscribers and private branch exchanges have to be accessed via packet-based transmission methods. Especially for the case of a failure of, for example, the subscriber terminals TNE or switching system-related devices or intervening communication paths, it must be made sure that substitute connections can be made and stable connections can be maintained. This problem is solved by the present invention by providing a peripheral adaptation device, integrated into the periphery of the switching system, and being suitable for the adaptation of the messages used on the interface between subscriber terminal and peripheral adaptation device, to the requirements of the plurality of peripheral devices associated with the TNE port. Furthermore, software functions are provided for treating the failure of, for example, the subscriber terminal, the one peripheral adaptation device or one of the associated periphera devices of the switching system. The interaction of said failure treatment software functions controls the substitute connection and restart of failed peripheral devices, peripheral adaptation devices and communication paths to subscriber terminals.

CLAIM FOR PRIORITY

[0001] This application claims priority to International Application No.PCT/DE01/04238 which was published in the German language on Jun. 27,2002.

TECHNICAL FIELD OF THE INVENTION

[0002] The invention relates to a system and method for packet-basedaccess of classical ISDN/PSTN subscribers to a switching system.

BACKGROUND OF THE INVENTION

[0003] Subscriber line concentrators (Remote Switching Units, RSU) orsubscriber access networks (Access Networks, AN) are used to connectconventional analog and ISDN subscribers and private branch exchanges.Both represent switching-center-external devices that are connected viaconcentrating interfaces to the peripheral devices of the exchange.

[0004] In line with their respective definition, the subscriber lineconcentrators/subscriber access networks have clearly establishedmechanisms for controlling the subscriber signaling to the peripheralequipment of the switching system. Signaling facilities for controllingthe subscriber line concentrators/subscriber access networks themselvesare provided at the same time. These affect, for example, the connectionof speech channels of the subscriber connection or of the extension tospeech channels of the interface of the subscriber line connectionconcentrator/subscriber access network to the peripheral equipment ofthe switching node. The operating status of the subscriber connectionand extension are also matched on this path between the subscriber lineconcentrator/subscriber access network and the switching system.

[0005] The exchange of subscriber signaling and control information isnormally message-based in the manner specified by the interfacedefinition. Typically, the complete interface is PCM-based and certaintime slots are reserved for message-based transmission ofsubscriber/extension signaling and control information.

[0006] The V5.2 interface is an example of a concentrating interfacebetween a subscriber access network and a local exchange. This providesthat ISDN signaling, ISDN packet data on the D channel and message-basedanalog signaling (PSTN) are transmitted in time slots of the interfacedefined in accordance with definable standard predetermined time slotsof the interface. For control of the subscriber access network,signaling protocols are provided that affect the forwarding ofinformation through the subscriber access network, the matching of theport and PCM route states and also the substitute switching of failedsignaling channels.

[0007] With regard to the definition, proprietary message-basedconcentrating interfaces can differ substantially from thespecifications of the V5.2 standard. All message-based interfaces tosubscriber line concentrators/subscriber access networks have somethingin common, they transmit subscriber signaling information (ISDNsignaling messages, ISDN packet data, PSTN messages) as well as thecontrol information for routing or for port status matching in certaintime slots of a TDM-based interface.

[0008] The convergence of packet-based networks and TDM networks leadsto a situation where conventional analog and ISDN subscribers andprivate branch exchanges have to be accessed using packet-basedtransmission methods.

[0009] A highly efficient access to the Internet can be achieved viaxDSL routes to the subscriber connection or via cable networks. Thismakes sufficient bandwidth available in the subscriber area to be ableto additionally handle narrowband conventional telephony/fax traffic viathe same access line. From the point of view of the subscriber,additional connectability of conventional subscriber terminals andprivate branch exchanges should be possible. In addition, all thesubscriber performance features known from the conventional PSTN/ISDNnetworks should still remain available. The user data necessary forswitching is, however, transmitted packet-based, in contrast to thesituation of a subscriber line concentrator/subscriber access network.The same applies to the signaling.

[0010] In this situation, the problem arises of connecting conventionalsubscribers or extensions (i.e. POTS, ISDN BA, ISDN PRI) that areswitched via subscriber terminals (e.g. IAD of an XDSL route, set-topbox of a cable network) with access to a packet network, in such a waythat all conventional subscriber performance features (including Dchannel packet data) are available in principle. Furthermore, thereusability of the hardware and software functions of a conventionalexchange should be retained. It should be possible to supply user dataflows, preferably packet based, or, as an option, via TDM technology tothe exchange, and transmit signaling information and ISDN-D channelpacket data packet-based to the exchange.

[0011] According to the prior art, this problem is solved by controllingthe aforementioned conventional subscribers as part of a subscriberaccess network. This has central components (such as IAT) that convertthe narrowband user data flow to TDM technology and prepare signalingand user data flows in the form of a V5.2 interface. The user data flowsare then processed in a conventional local exchange of the PSTN/ISDNnetwork. The input and output flows of broadband traffic are controlledby suitable upstream multiplexers. The relevant conditions areschematically shown in FIG. 1.

[0012] Accordingly, a subscriber access network AN is shown thatsupplies information on a plurality of subscriber terminals to theperipheral devices of an exchange LE. A device IAD that supportsspecific functions of the xDSL transmission method is provided as asubscriber access device. In a multiplexer DSLAM, narrowband informationis separated from broadband information and the xDSL route is closed.The speech and signaling information is applied, IP based, via an ATMnetwork as a carrier of a device IAT that forms the head end of thesubscriber access network AN. The latter passes the speech and signalinginformation via a V5.2 interface to a local exchange LE.

[0013] The advantages of the concept shown here are on the one hand theuse of an existing concentrating interface and on the other hand theavailability of all the subscriber performance features supported by theexchange. The decisive disadvantage on the other hand is in the use ofTDM technology in an exchange operating in an environment of convergingnetworks. There is also a deterioration of the speech quality due tothe, sometimes avoidable, conversion of the user data flow between TDMtechnology with Codec G.711 and the packet-based transmission by meansof a generally compressing Codec such as G.723.1.

SUMMARY OF THE INVENTION

[0014] The the invention shows conventional subscribers connected to anexchange using simple means via packet-based transmission methods andstable connections being maintained in the event of failure ofcommunication paths.

[0015] One advantage of the invention is that in the event of loss ofcommunication with the exchange the subscriber terminal near thesubscriber automatically attempts to re-establish this through severalavailable paths. Impermissible provision of switching resources, forexample the switching of a user channel to a remote subscriber is alsoautomatically terminated by the subscriber terminal device in the eventof loss of communication between the subscriber terminal device and theexchange.

[0016] Another advantage is that the exchange actively carries out acyclical check for availability of subscriber terminal devices, with, inparticular, ports at subscriber terminal devices identified asunavailable and ports with a switching activity (e.g. ports withconnected user channels) being checked. This results in a current statuspicture of the availability in the switching system and thus reduces thedummy load that would arise due to attempts to connect unavailableports. Furthermore, ports can, after repair, be automatically andquickly switched again to a state where they are available for switchingand connections already switched, by means of which one of theparticipating user terminal devices can no longer be reached bysignaling by the switching system, can be quickly and reliably cleareddown and the associated call charge metering thus stopped.

[0017] It is also advantageous that in the event of failure of aperipheral component of the switching system necessary for switching aport to a subscriber terminal device, switching resources of directlyaffected connections can be released. Connections can, however, continueto be maintained in a stable voice status, generally even through afailure situation, by requesting the switching status in the subscriberterminal devices and the participating media gateways.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The invention is explained in more detail using an exemplaryembodiment.

[0019] In the drawings:

[0020]FIG. 1 shows the relationships in the subscriber access networkaccording to the prior art.

[0021]FIG. 2 shows a concentrating interface with forced user dataconversion.

[0022]FIG. 3 shows a concentrating interface without forced user dataconversion.

DETAILED DESCRIPTION OF THE INVENTION

[0023]FIG. 2 shows a subscriber terminal device TNE with theconventional subscriber interfaces (a/b wire, S0, S2M). This terminatesthe physical connection lines of POTS, ISDN BA and ISDN PRI. Thesubscriber terminal device TNE is essentially identical to that inaccordance with the prior art, shown in FIG. 1. It has access to atleast two peripheral adaptation devices PAE of the exchange, with thisaccess being packet-based.

[0024] The peripheral adaptation devices PAE also shown here areperipheral components of the exchange. They have access to the messagedistribution system MB of the exchange. In addition, there can also beaccess to the switching network SN, with it being possible for PCM-basedinterfaces to be present at the peripheral adaptation device PAE as analternative.

[0025] Finally, peripheral devices PE of the exchange with access to themessage distribution system MB and switching network SN are provided. Aplurality of peripheral devices PE assigned to a concentrating interfaceprovides the switching function for this concentrating interface. Forthis purpose, a peripheral device PE in conventional use terminatesseveral PCM paths of this concentrating interface. If ISDN packet datais supported on the D channel, the transfer function for D channelpacket data to the packet handler interface is also provided by theaforementioned plurality of peripheral devices PE assigned to theconcentrating interface.

[0026] When a subscriber terminal device TNE is switched on, it attemptsto establish communication with one of the peripheral adaptation devicesPAE associated with it. The packet addresses of the associatedperipheral adaptation devices PAE in this case can be stored locally inthe subscriber terminal device TNE. Optionally, they can be requestedwhen the management system responsible for the network is started up. Ifthe communication with the peripheral adaptation device PAE in questionfails, a new communication attempt with a further associated peripheraladaptation device PAE takes place. The communication attempt with one ofthe peripheral adaptation devices PAE is cyclically repeated in theevent of failure.

[0027] When the communication to a peripheral adaptation device PAE isestablished, subscriber signaling takes place transparently for ISDNsubscribers and extensions. This means that messages arriving via the Dchannel are sent packet-based in the direction of the peripheraladaptation device PAE. Messages sent to the peripheral adaptation devicePAE contain the packet address of the subscriber terminal device TNEsupplemented by the identifier of the relevant port or packet address,from which the transmitting D channel is clearly shown. Messages sentfrom the peripheral adaptation device PAE to the subscriber terminaldevice TNE include the packet address of the subscriber terminal deviceTNE supplemented by the identifier of the relevant port or a packetaddress from which the receiving D channel is clearly derived.

[0028] Signaling messages and packet data on the D channel aretransmitted in the same way. Transmission of the ISDN L2 can take placeunprotected, which is completely adequate, particularly in good packetnetworks. To improve the transmission quality (message sequence,delays), the ISDN L2 is preferably completed in the subscriber terminaldevice TNE and a protected protocol is used between this and theperipheral adaptation device PAE.

[0029] For subscriber access networks with analog signaling, the linesignals in the subscriber terminal device TNE are converted to switchingmessages or, in the opposite direction, switching messages are convertedto line signals. These are exchanged in the same way between thesubscriber terminal device TNE and the peripheral adaptation device PAEas is the case for signaling messages of the ISDN subscriber to thesubscriber terminal device TNE. If necessary, a protocol different fromthe ISDN case can be used. The analog port can be addressed using apacket address for each analog port or via a packet address for severalanalog ports at the subscriber terminal device TNE, supplemented by aport identifier.

[0030] Switching orders for a channel for a port at the subscriberterminal device TNE and, if necessary, the availability status of theport, are exchanged between the subscriber terminal device TNE andperipheral adaptation device PAE. A packet-based protocol that coversthe aforementioned function is used for this purpose.

[0031] If the concentrating interface of the exchange is formed in sucha way that a port has access to the switching system via severalcommunication channels at the same time (such as for example is the casewhen operating with load sharing), communication links between thesubscriber terminal device TNE and several peripheral adaptation devicesPAE are established and simultaneously used in this present sense.

[0032] To simplify the description, only the case of the assignment of aport to a maximum of one communication for ISDN signaling, ISDN Dchannel packet data and/or PSTN signaling is considered in each case,all of which are transmitted via the same peripheral adaptation devicePAE. If an existing communication link via a peripheral adaptationdevice PAE is broken off, the subscriber terminal device TNE cyclicallyattempts to reestablish a communication link with a different peripheraladaptation device PAE. To do this, it stops the packet-based user dataflows associated with the active ports.

[0033] The functions of the peripheral adaptation device PAE serve toadapt the messages used on the interface between the subscriber terminaldevice TNE and peripheral adaptation device PAE to the needs of theconcentrating interface assigned to the TNE port.

[0034] Thus, particularly the address conversion between the addressingused for the TNE port and the exchange-internal address of the porttakes place at the concentrating interface assigned to the port.Furthermore, the protocol conversion of the subscriber signaling of themessages used in the direction of the subscriber terminal device TNE tothe protocol used for the particular signaling channels of theconcentrating interface is also undertaken.

[0035] This enables the forwarding of the ISDN signaling data betweenperipheral adaptation devices PAE and the peripheral devices PE. Thistakes place, TDM-based, via the switching network to the peripheraldevices PE, that terminate the respective signaling channels. To thisend, the system-internal NUC connections (nailed up connections)established at system runup are used. The distribution of the signalingmessages of the subscriber terminal device TNE to a plurality of suchfixed NUC connections takes place by means of the associatedconcentrating interface, the port address and the message type. If themessage distribution system supports a message transfer of adequateperformance between the peripheral device PE and peripheral adaptationdevice PAE, the message transmission by means of NUC and the switchingnetwork can also be omitted, and as an alternative the messagedistribution system can be used to transmit the signaling messagesbetween the peripheral device and peripheral adaptation device.

[0036] In this way, the peripheral adaptation device PAE creates theconditions whereby in the peripheral device PE associated with theconcentrating interface of the switching system the signaling of thesubscribers to the subscriber terminal device TNE occurs in the samemanner as if it had been carried via an intervening subscriber accessnetwork AN using TDM technology. Signaling data is processed in thenormal manner in the concentrating interface. The D channel packet datais forwarded to the packet handler interface.

[0037] The signaling required for the control of the concentratinginterface necessary to effect switching and matching of the port statusalso takes place via a peripheral adaptation device PAE, with this alsobeing carried out via an NUC or via the message distribution system.

[0038] Two types of concentrating interfaces are enabled by means of theaforementioned method.

[0039] The first is, as shown in FIG. 2, where it always enters the userdata channels of the ports at the subscriber terminal device TNE via amedia gateway MG in a peripheral device PE assigned to the call forswitching. This type of connection particularly provides all thesubscriber performance features for the port (concentrating interfacewith forced user data conversion).

[0040] The second type of concentrating interface dispenses with, asshown in FIG. 3, the unconditional conversion of the user channel to TDMformat and thus enables the direct exchange of user data between twosubscribers at the subscriber terminal device TNE by bypassing theexchange. This can have limitations with regard to the availability ofthe subscriber performance features (concentrating interface withoutforced user data conversion).

[0041] If the peripheral adaptation device PE when establishing aconnection outputs switching orders in the direction of the subscriberline concentrator, subscriber access network, these are converted in theperipheral adaptation device PAE to setting instructions to thesubscriber terminal device TNE and the interposed media gateway MG.

[0042] If more complex subscriber terminal devices (TNE variants), thathave to be combined in shelves or cabinets and perhaps use higher-levelsubscriber functional units and transmission devices, are used, thefunctionality of a subscriber access network required for this can alsobe provided by the peripheral adaptation device PAE. The data structuresrequired for the alarm and maintenance functions are held and maintainedin the peripheral adaptation device PAE. The necessary interface to themanagement system is held separate from that of the switching system,for advantageous reduction of the complexity of the overall system, sothat then the functions of a local exchange as well as those of a localdistribution network are provided without the latter being provided as aseparate device.

1. Method for connecting conventional analog and ISDN subscribers to aswitching system, with the subscriber signaling between a subscriberterminal device (TNE) and the switching system being transmitted,packet-based, via a network and with a plurality of such subscribersbeing assigned in each case to a common set of peripheral devices (PE)of the switching system, characterized in that, at least one peripheraladaptation device (PAE) is provided, that is arranged in the peripheryof the switching system and is used for the adaptation of the messagesused on the interface between the subscriber terminal device (TNE) andperipheral adaptation device (PAE) serves the requirements of the set ofperipheral devices (PE) assigned to the TNE port, software functions fordealing with failures in the subscriber terminal device (TNE) of atleast one peripheral adaptation device (PAE) and the associatedperipheral devices (PE) of the switching system are provided, due to theinteraction of these software functions for dealing with failures thealternative routing and restoration of failed peripheral devices (PE),peripheral adaptation devices (PAE) and communication paths tosubscriber terminal devices (TNE) are controlled.
 2. Method inaccordance with claim 1, characterized in that, in the event of loss ofcommunication via a peripheral adaptation devices (PAE) communicationvia a further peripheral adaptation device (PAE) is established from thesubscriber terminal device (TNE).
 3. Method in accordance with claim 1,2, characterized in that, in the event of failure of communication viaall the peripheral adaptation devices (PAE) assigned to it, thesubscriber terminal device (TNE) cyclically attempts to establishcommunication via a further peripheral adaptation device (PAE), theassociated switching resources are released and the activated switchingof user data flows of their connections are terminated.
 4. Method inaccordance with claims 1 to 3, characterized in that, the failure andthe restoration of availability of a connection at the subscriberterminal device is signaled to the switching system by the subscriberterminal device (TNE) via the communication with the peripheraladaptation device (PAE) and the picture of the status of a connection isheld in the exchange and the switching availability of the connection isdescribed in the switching system.
 5. Method in accordance with claim 4,characterized in that, the MGCP protocol or H.248 is used to signal thestatus of a connection at the subscriber terminal device (TNE) to theswitching system.
 6. Method in accordance with one of the precedingclaims, characterized in that, the connections reported at thesubscriber terminal device (TNE) as failed are cyclically checked by theperipheral adaptation device (PAE) for restoration of availability. 7.Method in accordance with claim 6, characterized in that, the MGCPprotocol or H.248 is used to check the status of a connection at thesubscriber terminal device (TNE) by means of the peripheral adaptationdevice (PAE) of the switching system.
 8. Method in accordance with oneof the preceding claims, characterized in that, connections at thesubscriber terminal device (TNE) that are active with regard toswitching are cyclically checked for availability by the peripheraladaptation device (PAE), and if non-availability is determined, theswitching and transactions are cleared down and the call charge meteringfor the relevant connection is stopped in the exchange.
 9. Method inaccordance with claim 8, characterized in that, the MGCP protocol orH.248 is used for checking the active switching connections at thesubscriber terminal device (TNE) by means of the peripheral adaptationdevice (PAE) of the switching system.
 10. Method in accordance with oneof the preceding claims, characterized in that, in the event of failureof peripheral adaptation devices (PAE), stable connections aremaintained by the redundant storage of switching states in a redundantperipheral adaptation device (PAE) or by recovery of the switchingstates by interrogating the participating subscriber terminal devicesand media gateways after switching to a further peripheral adaptationdevice (PAE).
 11. Method in accordance with one of the preceding claims,characterized in that, in the event of failure of a peripheral device(PE), the through switching of connections that can no longer beoperated is dealt with by utilizing the storage of the switching statesin the peripheral adaptation devices (PAE) or by recovery of theswitching states by interrogating the participating subscriber terminaldevices and media gateways.
 12. Method in accordance with claim 10 or11, characterized in that, the MGCP protocol or H.248 is used for therecovery of the switching states by interrogating the participatingsubscriber terminal devices (TNE) and media gateways.
 13. Method inaccordance with one of the preceding claims, characterized in that, thefailure of a subscriber terminal device (TNE) is detected by cycliccommunication attempts of a peripheral adaptation device (PAE) and thenon-availability of the associated connections is depicted.
 14. Methodin accordance with one of the preceding claims, characterized in that,ports of a subscriber terminal device used in the switching system asconnections not available for switching are not used even forterminating calls.